Introversion is an operation on the valency of a transitive verb which blocks its undergoer argument position, thus detransitivizing it. In .a, the verb has its base valency, which is transitive. #b shows an introversive derivation, in this case by low tone on the root.

.a.Hwaan=e'k-uts'ik-ikPeedroh
YucatecJohn=TOPIPFV-SBJ.3shave-INCMPLPeter
John shaves Peter
b.Hwaan=e'k-uts'iik
John=TOPIMPF-SBJ3shave\INTROV(INCMPL)
John shaves (people)

The direct function of introversion is the valency change of the verb, which makes it impossible to mention an undergoer.

The ultimate function of introversion is to concentrate on the action of the actor by neglecting the involvement and identity of the undergoer. Although this makes it appear that there is no undergoer, many transitive verbs designate a situation core which is inconceivable without an undergoer. If John is hunting, this does not mean that there is nothing that he hunts; if one were hunting nothing, one would not actually be hunting. The point is that (the nature or identity of) the undergoer is of no concern.